As sea level rises, it will push saltwater into aquifers that supply Floridians' drinking water. The problem will be exacerbated because water levels in the aquifers already have been lowered by pumping — to provide drinking water.

A tide gauge at St. Petersburg shows the highest average monthly sea level rise by nine inches between 1948, the first full year of recorded tide data, and 2012. That period coincided, of course, with heavy population growth, droughts and overpumping of groundwater, which worsened saltwater intrusion.

Growth predictions led to an effort to find alternative water sources, including a desalination plant. Two private firms involved in the project went bankrupt. Since regional utility Tampa Bay Water began operating it in 2007, the plant has been plagued with repairs and typically doesn't regularly produce anywhere near its 28-million-a-day full capacity. Part of the reason is that desalinated water costs four times as much as groundwater. "Desalination is our most expensive water," says Tampa Bay Water spokesman Brandon Moore.

Utilities skittish about desalinated water may not have many choices. Barry Heimlich, a research affiliate with Florida Atlantic University's Center for Environmental Studies who has studied sea level rise and its impact, says communities in southeast and southwest Florida will begin having significant problems with flooding and saltwater intrusion in the next 20 to 30 years if they don't invest in drainage and salt-proofing the infrastructure, he says.

"Our ability to live in south Florida is totally dependent on the fact that our forefathers figured out how to drink the water in order for us to live here," Heimlich says. "And now we've got to protect that."